The process of this invention concerns the hydroformylation of alpha,beta-unsaturated nitriles to produce the corresponding 2-cyanoaldehydes. In particular, the process of the invention concerns the use of a rhodium-ligand catalyst complex to produce selectively the 2-cyanoaldehydes from the alpha,beta-unsaturated nitriles.
The alpha,beta-unsaturated nitriles, such as acrylonitrile, have been hydroformylated previously. British Pat. No. 910,767, granted Nov. 21, 1962, describes the hydroformylation of acrylonitrile using dicobalt octacarbonyl. The process produces a relatively high yield of 3-cyanopropionaldehyde. In addition to 3-cyanopropionaldehyde, various by-products are formed. Kato et al. (Ajinomoto Co., Kawasaki) report in "Kogyo Kagaku Zasshi" 65, 184-7 (1962) that the hydroformylation of acrylonitrile in methanol produces 3-cyanopropionaldehyde as the principal product, and propionitrile, propanol, gamma-hydroxybutyronitrile, propylamine, ammonia and possibly allylamine as by-products.
The 2-cyanoaldehydes are valuable solvents and chemical intermediates. For instance, 2-cyanopropionaldehyde can be hydrogenated and dehydrated to produce methacrylonitrile. There are several processes for preparing 2-cyanoaldehyde reported in the art. For instance, Pino et al. (Polytecnico, Milan), in "Rend. 1st Lombardo Sci., Pt. I, Classe Sci. Mat. e Nat." 88, 378-88 (1955) report the production of 2-cyanopropionaldehyde by the ring-opening reaction of beta-methylisoxazole. Borsche et al in "Annalen" 512, 97-111 (1934) report that the condensation of ethyl nitrile and ethyl formate produce 2-cyanopropionaldehyde.
In accordance with U.S. Pat. No. 3,579,562, alpha- and beta-formyl nitriles are also allegedly produced by the formylation of methacrylonitrile using uncomplexed metallic rhodium, ruthenium or iridium or their salts or oxides. It is stated in the aforesaid patent that when products are desired containing primarily the alpha-formyl compounds, the hydroformylation reaction should be conducted at temperatures below 100.degree. C. On the other hand, when the beta-compounds are desired, it is stated that the hydroformylation reaction should be carried out at temperatures above 100.degree. C.